<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>发送post请求</button>
    <script>
        document.querySelector("button").onclick = function () {
            let xhr =new XMLHttpRequest();
            xhr.open("post","/postdata")
            xhr.setRequestHeader("content-type","application/json");//发送json数据，内容和头部要对应上
            xhr.send(JSON.stringify({type:2}));  
            xhr.onload = function () {
                if(xhr.status>=200&&xhr.status<300){
                    console.log(xhr.responseText);
                }
            }
        }
    </script>
</body>
</html>